Answer
Hydrogen is moving faster.
Work Step by Step
Recall that $H_2$ weights $3.3 \times 10^{-27}$ kg, and Sulfur Dioxide weighs $1.1 \times 10^{-25}$ kg. Thus:
$ v_ = \sqrt{\frac{3(T)}{m}}$
For Hydrogen:
$ v = \sqrt{\frac{3(1.4 \times 10^{-23})(75)}{3.3 \times 10^{-27}}} = 967 m/s$
For Sulfur Dioxode:
$ v = \sqrt{\frac{3(1.4 \times 10^{-23})(350)}{1.1 \times 10^{-25}}} = 370 m/s$
